Wellbores which are drilled in the earth formation for hydrocarbon exploration and production purposes become ever deeper and more complex in geometry as many times curved, inclined or horizontal sections are included. Such deep and complex wellbores impose stringent requirements on the drill strings used.
So far the only proven successful method of drilling ERD wells is by continuous drill string rotation. However with increasing reach the build up of large friction forces between the drill string and the wellbore wall often hamper adequate wellbore operations.
Beyond a certain reach, drilling in the sliding mode, required for bit steering, becomes even impossible. Because of this, rotary steerable drilling systems are currently being developed. Owing to the high inclination of ERD wells, these systems require long and heavy bottom hole assemblies ("BHAs") comprising drill collars and heavy weight drill pipe sections to get the required weight on bit for efficient drilling.
This all adds to the surface torque for string rotation and results in heavy drill string designs finally reaching the mechanical limits of currently available equipment at around 10 km of reach. Pulling the drill string out of hole ("POOH") virtually becomes impossible in these wells mainly because of string yield. The present invention provides an ERD system which makes it possible to break through the 10 km limit.